Digital added main line system

ABSTRACT

A method and apparatus for transmitting and receiving multiple telephone transmission signals over a single twisted pair. An analog signal from a local switching station is converted to an 80 kbits/sec signal for transmission over a twisted pair. A remote terminal converts the 80 kbits/sec signal back into a conventional analog signal for use in conventional telephone, facsimile or other related equipment.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

The present invention relates to the field of telephone communication.More particularly, in one embodiment the present invention provides amethod and apparatus for simultaneously transmitting information frommultiple phone connections over a single twisted pair line.

Techniques for transmission of multiple voice or data signals over asingle phone line are well known in the telecommunications industry andare commonly referred to as concentration techniques. In the past,frequency division multiplexing was the most commonly used technique forsimultaneous transmission of multiple voice or data signals over asingle line. Frequency multiplexing techniques are still commonly usedin, for example, wideband transmission media.

Digital time division multiplexing techniques have been used since the1960's and have become the most common concentration technique in, forexample, interoffice circuits. An entire family of T-carrier (Trunkcarrier) systems such as T1, T1C, T1D, T2, and T4, have been developedfor concentration of multiple voice and data signals over a common line.Digital concentration techniques are described in, for example, Bellamy,Digital Telephony, Wiley and Sons, 1982, which is incorporated herein byreference for all purposes.

Digital communication has become relatively standard in, for example,intraoffice trunks. One example of a method for transmitting multiplevoice or data signals over a single two- or four-wire transmission lineis disclosed in Kaiser et al., "Digital Two Wire Local ConnectionProviding Office Subscribers With Speech, Data, and New TeleinformationServices," ISSLS, Mar. 20-24 (1978). In Kaiser et al., telephone data,viewdata, telecopier information and the like are transmitted in adigital fashion over a two- or four-wire line to a local exchange.Digital data are transmitted in data bursts which are later expanded andrecovered using, e.g., time division multiplexing techniques.

Despite advances in the multiplexing techniques a variety of problemsremain. For example, some multiplexing techniques continue to requirecomplex and, therefore, uneconomical equipment. This equipment isparticularly unsuitable for individual or small office users. Further,when applied to residential users, small office users, and the like,some systems require that the user provide a power source such as atransformer connection to a 120 v. power source, a battery power sourceor the like. Some systems require that the user replace existingtwo-wire connections with less conventional connections and/or arelimited in the distance of twisted pair line over which information maybe transmitted. In spite of certain advances in the ability to transmitmultiple voice and data signals over single twisted pairs, most localswitching units continue to provide a single analog signal over a singletwisted pair to a typical home or office.

It would be desirable to provide an improved and more economical methodand associated apparatus for multiplexing multiple phone lineconnections over a single twisted pair connection especially for use inproviding multiple phone lines over a single twisted pair into a home oroffice from a local telephone exchange.

SUMMARY OF THE INVENTION

An improved method and apparatus for transmission of multiple signalsover a single twisted pair is disclosed. In a preferred embodiment theinvention provides for transmission of multiple voice and/or datasignals over a single twisted pair from a local telephone exchange to asubscriber.

In one embodiment, the invention provides apparatus for concurrentlyreceiving "n" telephone signals over a twisted pair, where "n" isgreater than 1, comprising at a first location, means for receiving adigital signal from a local telephone exchange, the digital signalrepresenting said "n" telephone signals in digital form; means forconverting the digital signal into a first higher-rate binary signal;and means for converting the higher-rate binary signal into "n" analogsignals for use in equipment at said first location. The digital signalmay, for example, be a 4B3T or quaternary signal.

A method of transmitting "n" telephone signals over a twisted pair froma first location is also provided. The method includes the steps ofconverting "n" analog telephone signals to a binary signal; convertingthe binary signal to a lower-rate digital signal; and transmitting saidlower-rate digital signal over said twisted pair to a second location.In an alternative embodiment, the method includes the steps of inputtinga digital signal from a second location over a twisted pair to a firstlocation; converting the digital signal to a higher-rate binary signaland converting the higher-rate binary signal to "n" analog signals foruse in telephone equipment at the first location.

A kit for concurrent transmission of a plurality of telephone signalsover a single twisted pair from a subscriber location to a localswitching station is also provided. The kit includes master equipmentincluding a means for conversion of quaternary 80 kbits/sec signals toand from a higher-rate binary data stream; a SICOFI for conversion ofthe binary data stream from and to analog signals; and remote terminalequipment including a means for conversion of quaternary 80 kbits/secsignals from and to binary higher-rate data streams; a means forconversion of binary higher-rate data streams from and to analog signalsand a means for two-wire to four-wire conversion.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an overall block diagram of a remote terminal (RT) accordingto one embodiment of the invention;

FIG. 2 is an overall block diagram of a master according to oneembodiment of the invention; and

FIGS. 3a to 3e are block diagrams of the logic used in microprocessor inthe RT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS CONTENTS

General

Digital Data Transmission

A. Hardware

B. Software/Microprocessor Functionality

III. Power Management

I. General

An improved method and apparatus for transmitting and receiving dataover a single twisted pair wire are disclosed herein. The method andapparatus will find particular utility and is illustrated herein as itis applied in the transmission of multiple voice, data, and alarmsignals over existing twisted pair lines which are used to connecthomes, offices, and the like to local switching facilities, or centraloffices, but the invention is not so limited. The invention will finduse in a wide variety of applications where it is desired to transmitmultiple voice and/or data signals over a single twisted pair including,for example, facsimile, computer data, alarms, and/or low-speed videosignals.

II. Digital Data Transmission

A. Hardware

FIG. 1 provides a block diagram of a remote terminal (RT) according toone embodiment of the invention. The RT would be placed in, for example,a home, office or other subscriber facility for transmission and/orreception of voice or data signals over a single twisted pair line 1 toand from a local telephone exchange. A plurality of phones or othersubscriber equipment would utilize analog signals produced by the RT andprovide analog signals to the RT for transmission over the twisted pair.

A signal DCL From Master enters or leaves the RT over the conventionaltwo-wire line 1, which may be the type commonly used in households,offices, or the like. As will be readily apparent to those of skill inthe art, the signal could either be a transmitted voice or data signalfrom the master. The invention will be illustrated herein as it appliesto the RT primarily with regard to an incoming signal, but the processis similarly applied in reverse to provide voice and data signals fromthe RT to the master.

The signal DCL From Master, representing in digital form a voice or datasignal, enters a line transformer 2 for isolation and for impedancematching. The voice or data signal entering the line transformer 2 is an80 kbits/sec signal having one of four voltage levels. While theinvention is illustrated herein with regard to the preferred 80kbits/sec signal, it is believed that the invention herein would findutility using signals of between about 50 and 100, and preferablybetween 70 and 90 kbits/sec. The use of an 80 kbits/sec 2B1Q ANSA lineprotocol signal permits the transmission and reception of voice and datasignals over extended lengths of twisted pair wires, e.g., 1,000,15,000, 20,000 feet or more, without smearing, i.e., signal quality overlarge distances is improved because the lower frequency 80 kbit signalmay be more readily separated.

The signal from the line transformer enters an ISDN EchoCancellation-Quaternary (IECQ) chip 4 via line 3a. The 80 ksymbol 2B1QINSA line protocol signal contains 160 kbits/sec of information and theIECQ chip 4 converts the 80 kbits/sec signal into a 160 kbits/sec binarysignal. The 160 kbits includes 16 kbits of line control information and144 kbits of user data. 112 kbits/sec of chip control information areadded to the data stream by the IECQ chip, resulting in 256 kbits/secdata stream from the IECQ chip and provided to ISDN CommunicationsController (ICC) multiplexing and data handling chip 6 over line 5a. TheICC operates on a clock signal (CLK) at, for example, about 520 kHz anda frame control signal (FSC) at, for example, about 8 kHz. CLK and FSCare provided over line 7.

Over a one-wire bus 13, the ICC chip 6 sends 8 bits of data on onechannel, 8 bits of data on the other channel, 8 bits of control, and 8bits of signal data to Codac Filter (SICOFI) 10, and then repeats,permitting substantially simultaneous transmission/reception of two ormore voice or data signals. Monitor data, ring data, and other datawhich the microprocessor poles are also made available to themicroprocessor.

SICOFI 10 converts the binary bits into analog signals in which bothfrequency and amplitude are modulated. The analog signals are thentransmitted over line 9a to Subscriber Line Interface Circuits (SLIC's)12a and 12b. SLIC's 12a and 12b are 4-wire to 2-wire converters andserve to increase the power available for utilization by thesubscriber's phone or other communication device by enpressing theanalog signal on high velocity DC. Conventional analog information isprovided to subscriber phones 17a and 17b from the SLIC's over lines 14aand 14b.

Ring inserts 16a and 16b are relays which close when it is desired for aphone to ring under the direction of the microprocessor. Power supply18, using a process more fully described below, provides general powerand ring power to the phones at appropriate times via a ring bus 20.Buffer 22 serves to interface local status and alarms.

Outgoing signals from the subscriber are processed in a similar butreverse method from incoming signals. In particular, analog signalsenter SLIC's 12a and 12b for two-wire to four-wire conversion via lines15. Signals from SLIC's 12a and 12b enter SICOFI 10 via lines 9b foranalog-to-binary 8-bit word conversion. These 8-bit words are,thereafter, converted in ICC 6 into a binary stream containing 160kbits/sec of user information (144 kbits of user data plus 16 kbits ofline control) for input to IECQ 4 via line 5b. IECQ 4 converts the 160kbits/sec signal to an 80 ksymbols/sec quaternary signal fortransmission to telephone company equipment over the twisted pair 1.

FIG. 2 is a block diagram of a master unit which would be placed in alocal switching unit, central office, or other telephone companyequipment at the terminus of a twisted pair wire 1 from a home, officeor the like. The function of the master is similar to that of the RT,but reversed; i.e., the master converts conventional analog signals fromlocal switch lines 50a and 50b to appropriate digital signals fortransmission over the twisted pair and converts digital signals from thetwisted pair to analog for transmission over local switch lines. Ofcourse, the master is not generally power constrained (due to itslocation and lack of need to provide ring capability) and may functionusing a conventional 48-volt power supply 52 from the local switchingunit.

Ring detects 54a and 54b detect an incoming ring signal from switchlines 50a and 50b by AC coupling. When a ring is detected themicroprocessor sends an appropriate ring signal in the line control dataso as to ring a line at the RT.

Incoming analog signals enter SICOFI 56 from the switch lines via lines55a where they are converted to digital, 8-bit words similar to those inthe RT described above. SICOFI 56 transmits to the ICC via bus 57. ICC58 serves a multiplexing and data handling function similar to that ofthe ICC in the RT and transmits 160 kbits/sec of user information (144kbits of user data plus 16 kbits of line control) to IECQ 60 via line59a for conversion to 80 kbits/sec quaternary signals for transmissionover twisted pair 1. The master similarly processes incoming digitalinformation from the RT in a reverse order. Line transformer 61 alsoserves an isolation function, receiving signals via line 63a.

The functionality of the master is overseen by a microprocessor 60,similar to the RT. A clock 62 provides timing information for themicroprocessor and the other components in master and, ultimately, theRT. Buffer 64 serves to interface status and alarms. Bus 66 serves toprovide an office system interface from system alarms.

Without in any way limiting the scope of the invention, Tables 1 and 2provide a list of commercially available components which are useful inoperation of the RT and Master respectively according to the aboveembodiments. It will be apparent to those of skill in the art that thecomponents listed in Tables 1 and 2 are merely representative of thosewhich may be used in association with the inventions herein and areprovided for the purpose of facilitating assembly of a device in accordwith the invention. A wide variety of components readily known to thoseof skill in the art could readily be substituted or functionality couldbe combined or separated. It should be noted that CMOS-based deviceshave been utilized where possible (e.g., the microprocessor) so as toreduce power consumption of the RT in particular.

                  TABLE 1                                                         ______________________________________                                        RT Components                                                                 ______________________________________                                        Line Transformer 2                                                                             13 mh, 1:1.32                                                IECQ 4           Siemens 2091                                                 ICC 6            Siemens 2070                                                 Microprocessor 8 Intel 80C49, 80C51 or 87C51                                  SICOFI 10        Siemens 2260, or 2060                                        SLIC 12          Erickson PBL 3764, or                                                         Harris equipment                                             Buffer 22        74HC244                                                      ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Master Components                                                             ______________________________________                                        Ring Detect 54    Siemens PSB 6620                                            SICOFI 56         Siemens 2260 or 2060                                        ICC 58            Siemens 2070                                                IECQ 60           Siemens 2091                                                Clock 62          74HC4060                                                    Microprocessor 60 Intel 80C51, 87C51 or 8048                                  ______________________________________                                    

B. Software/Microprocessor Functionality

Appendix I provides an assembly language program listing (Copyright,Unpublished Work, Raychem Corporation) for the RT microprocessor 8discussed above. The code is adapted for and has been used on an Intel80C51 microprocessor, although it will be apparent that the inventioncould be applied to a wide variety of such processors. Appendix II(Copyright, Unpublished Work, Raychem Corporation) provides a similarlisting for the code used in the microprocessor 60 in the master. Thiscode has been used in the Intel 80C51. Again, however, a wide variety ofmicroprocessors could be used herein without departing from the scope ofthe invention.

FIGS. 3a to 3e are flow charts illustrating the functionality of thesoftware used in the RT and Master, and provide an overview of thesoftware in Appendix 1 and Appendix 2. The left hand portion of FIG. 4aillustrates the power-up sequence used to initiate the system. Thesystem begins by resetting the microprocessor (8051) registers andmemory. The ISDN chip 2, the ICC, SICOFI's, and the like are reset andconfigured. Variables within the program are, thereafter, activated,timers are started, and 160 Hz interrupts are started. The program thenenters a main loop, which is illustrated in detail beginning on theright half of FIG. 4a.

Upon receiving a 160 Hz clock interrupt, the system reloads the clockcounter and, in the RT, reads any local alarms (such as alarms from aburglar alarm and the like). The system then reads the local hook statusand determines if a message has been transmitted over the link from theRT/Master. If a message has been transmitted over the link, the systemreads the message to determine the hook status (i.e., on or off hook)and any alarms. If there is not a message from the other end of thelink, the system determines if it has made more than a preset number ofpasses without a message from the other end of the link. If so, thetolerance count of consecutive messages missed is reset and an alarm isset which may be, for example, passed off to a CO.

In any event, the system then goes on to determine if it is ready totransmit across the link by checking a flag in the ICC. If not, asimilar test and reset procedure is followed to that described above forreceiving messages. If the link is ready to transmit, the messages areloaded and sent to the RT/Master from the Master/RT.

Referring to FIG. 3b, the system then determines if there has been anychange in the command/instruction (C/I) channel from the SICOFI. If not,the system determines if the link is down and, if not, continues on. Ifthe link is down, the system compares the number of passes to a limitand, if the link has been down for greater than that limit, resets alink missing tolerance count and issues a command to reactivate thelink.

If there has been a change on the C/I channel, the system thendetermines if the change has been an activation indication. If not, thesystem determines if the link was previously up and, if not, the loopcontinues. If the link was previously up, the SICOFI in the RT ispowered down, and the hook and alarm data for the far end are reset. Anindication is also provided to the user that both lines are down and thealarms are on. The missing tolerance count is reset and a command isthen issued to reactivate the link.

Referring to FIG. 3e, if the change on a C/I channel was an activationindication, the High-Level Data Logic Control (HDLC) transmission modeis set, the link transmitter and receiver are reset, and an indicationis provided that the link is up. The system then continues through themain loop.

In the master (or "COT" end) the main loop then determines if the offhook or local line request for line A is received. If so, an indicationis provided at the Master that line A is off the hook. A similar test isprovided for line B and displays are provided on LED's. The system thendetermines, for both lines, if the line is off the hook. For either linewhich is off the hook, a line is seized at the COT. The clock interruptroutine is then exited at the Master.

Referring to FIG. 3d, the main loop in the RT continues by copying thelocal hook status and far-end ring request to line status bytes. Lineservice routines for both lines are called and the clock interruptroutine is exited.

FIG. 3e illustrates the line service routine for the RT. A test is firstconducted to determine if the RT is in a ring stop mode. If so, a testis conducted to determine if a ring stop period has expired and, if so,the ring stop mode is cleared and the ring relay is deactivated. Thesystem then returns to the main loop.

If the system is not in a ring stop mode, it is determined if a ring isrequested. If a ring is requested, but the line is off the hook, theSICOFI is powered down to conserve power, and the line service routineis exited. If the line is not off the hook, it is determined if the lineis in the ring-active mode and, if so, a ring oscillator is toggled andthe line service routine returns to the main loop. An intermediate testis conducted, however, to determine if the other line is off the hook.If not, the ring relay is activated. However, if the other ring is inthe ring-active mode, the system returns to the main loop.

If a ring has not been requested, the line is not in the ring-activemode, and the line is not off the hook, the SICOFI is powered down andthe system returns to the main loop. If, however, the line is off thehook, the SICOFI is powered up for conversation. If a ring has not beenrequested and the line is in the ring-active mode, the ring stop mode isset and the ring oscillator is deactivated. The system then returns tothe main loop.

III. Power Management

The system described above provides multiple-line telephone services toa user over a single twisted pair without the need to provide a batteryor other current source at the RT. At the same time, the systemmaintains the line power within the limits proscribed by TR-TSY-000057standard AII in a standby mode and AIII during active line use.

Table 3 illustrates the power usage of the various components in thesystem in a standby mode, an active mode, a 1-ring mode, and a 1-active,1-ring mode. The data illustrated in Table 3 are based on a 16500-foottwisted pair using 26-gauge wire plus 1500 feet of 24-gauge wire.

Table 3 illustrates that by use of the method/apparatus disclosedherein, in the standby mode the system is well within AII limits.Specifically, about 430 milliwatts may readily be provided in a typicalsystem while remaining in AII limits, while only 373 milliwatts areneeded during standby. Similarly, the 2302 milliwatts needed for 1-ringand 1-active signals are well within the amount of power which may beprovided while staying within AIII limits.

                  TABLE 3                                                         ______________________________________                                        System Power Use (milliwatts)                                                         Mode                                                                  Component Standby  2-Active 1-Ring                                                                              1-Active, 1-Ring                            ______________________________________                                        Microprocessor                                                                          25        25       25    25                                         ICC       3         3        3     3                                          IECQ      300      300      300   300                                         SICOFI    3        120      120   120                                         SLIC      42        90       42    66                                         Loop      0        1176      0    588                                         Ring      0         0       1200  1200                                        TOTAL:    373      1714     1690  2302                                        ______________________________________                                    

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reviewing the above description. By wayof example the inventions herein have been illustrated primarily withregard to transmission of voice and data signals (POTS), but they arenot so limited. For example, the inventions could be applied in thetransmission and reception of radio and TV signals, telephoto, teletype,facsimile, and other signals. By way of further example, the inventionshave been illustrated above with reference to the simultaneoustransmission of two signals over a single twisted pair, but theinventions could readily be extended to transmit 3 or more signalssimultaneously over a single twisted pair. The scope of the inventionsshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

What is claimed is:
 1. A digital added main line comprising:a) a remoteterminal for use at a subscriber location, said remote terminalcomprising:i) a remote terminal ISDN echo cancellation integratedcircuit for converting digital quaternary signals on a twisted pair lineto binary signals and converting binary signals to quaternary signalsfor transmission over said twisted pair line; ii) a remote terminal ISDNcommunications controller integrated circuit coupled to said remoteterminal ISDN echo cancellation circuit for adding and removing controlinformation to and from a data stream from and to said remote terminalISDN echo cancellation circuit; and iii) a remote terminal subscriberinterface codac filter integrated circuit coupled to said remoteterminal ISDN communications controller circuit for converting binarysignals from and to said remote terminal ISDN echo cancellation circuitto and from at least two analog signals for use in subscriber equipment;and b) a master comprising:i) a master subscriber interface codac filter(SICOFI) integrated circuit for conversion of analog signals at a localswitch to and from digital binary signals; ii) a master ISDNcommunications controller integrated circuit coupled to said masterSICOFI for adding and removing control information to and from a datastream from said SICOFI; and iii) a master ISDN echo cancellationintegrated circuit coupled to said master ISDN communications controllerfor conversion of digital binary signals to and from quaternary signalsfor transmission over said twisted pair.
 2. A digital added main line asrecited in claim 1 wherein said remote terminal is located at a terminusof said twisted pair at a home or office and said master is located at atelephone company switch.
 3. A digital added main line as recited inclaim 1 wherein said remote terminal and master ISDN echo cancellationcircuits are adapted to transmit and receive substantially 80ksymbols/sec signals.
 4. A digital added main line as recited in claim 1wherein said remote terminal and master ISDN communications controllersare adapted to transmit and receive substantially 160 kbits/sec signals.5. In a system for transmission of a single analog signal from atelephone company location to a subscriber location over a twisted pair,a method of converting said system to a system for multiple signaltransmission over said twisted pair comprising:a) installing masterequipment at said telephone company location, said master equipment:i)inputting multiple incoming telephone company analog signals fromtelephone company equipment and outputting multiple outgoing telephonecompany analog signals to said telephone company equipment; ii)converting said multiple incoming telephone company analog signals to amultiplexed outgoing 2B1Q signal and converting a multiplexed incoming2B1Q signal to said multiple outgoing telephone company analog signals;and iii) transmitting said multiplexed outgoing 2B1Q signal over saidtwisted pair to said subscriber location and receiving said multiplexedincoming 2B1Q signal; and b) installing a remote terminal at saidsubscriber location, said remote terminal:i) inputting said multiplexedoutgoing 2B1Q signal-from said twisted pair and outputting saidmultiplexed incoming 2B1Q signal on said twisted pair; ii) convertingsaid multiplexed outgoing 2B1Q signal to multiple outgoing subscriberanalog signals and converting multiple incoming subscriber analogsignals to said multiplexed incoming 2B1Q signal; and iii) transmittingsaid multiple outgoing subscriber analog signals to subscriber equipmentand receiving said multiple incoming subscriber analog signals from saidsubscriber equipment.
 6. The method as recited in claim 5 wherein saidtwisted pair has a length greater than 1,000 feet.
 7. The method asrecited in claim 5 wherein said twisted pair has a length greater thanabout 15,000 feet.
 8. The method as recited in claim 5, said remoteterminal further converting said multiple outgoing subscriber analogsignals from a four-wire format to a two-wire format and converting saidmultiple incoming subscriber analog signals from a two-wire format to afour-wire format.